Hematopoietic stem/progenitor cell (HSPC) interactions with the cellular microenvironment or niche provide adhesion based signaling, which is necessary for the maintenance of HSPC proliferation, differentiation, and survival. Despite the clinical successes from using HSPC transplantation for the treatment of blood cancers, the mechanisms that regulate HSPC interactions with their microenvironment remain largely unknown. As such, it is critical that we identify the mechanisms and molecules that regulate HSPC adhesion to the microenvironment to provide clinical targets to enhance HSPC transplantation therapies. The objective of this proposal is to determine the mechanism by which CD82 regulates integrin-mediated HSPC adhesion by modulating integrin clustering and activation. We will test the hypothesis that CD82 regulates HSPC adhesion and homing by modulating integrin clustering and activation. In Specific Aim 1, I will use Western blot and flow cytometry analyses to quantify ?1 activation levels in response to ligand to address how CD82 expression and specific CD82 mutations regulate ?1 activation. Furthermore, I will use super-resolution imaging (SRI) to resolve the membrane protein organization of total and activated ?1 integrins. For Specific Aim 2, I will use mutant CD82 and primary human CD34+ cells in adoptive transfer experiments to assess how CD82 regulates the homing and niche localization of HSPCs. Additionally, I will use SRI to quantify the molecular organization of B1 and CD82 at the HSPC contact site with niche cells to identify how CD82 regulates integrin organization in response to the microenvironment. This proposal is significant because we expect to identify CD82 and its regulatory partners as molecular targets to enhance HSPC transplantation therapies. This proposal is innovative in that it combines cutting-edge imaging techniques with in vivo analyses to provide a multi-scale understanding of how tetraspanins regulate HSPC homing. Moreover, my study takes a unique approach by targeting an upstream regulator of integrins, CD82, for the control HSPC homing. As such, this proposal will provide insight into novel molecular regulators that can be targeted to enhance the adhesive properties of HSPCs prior to transplantation.